Android Thread Concurrent running threads notify between them

Question

I want to execute the method uploadingDone() after completion of all three threads. The flags are working most of time correct. In rare case all three flags set to true and BLOCK1 get executed twice. All three threads are doing different tasks on different data ( No Concurrent modification can occur).

Can I eliminate the flags with any native function on thread?

All three threads to be run in parallel(Mandatory Requirement.). BLOCK1 should be called only once .

private synchronized void uploadingDone(){

    if( isItemUploaded && isListUploaded && isStoreUploaded){
        uploadingDone = true;
         //<BLOCK1>
        //TODO move to next screen
    }else{
        Log.i(TAG, "uploadingDone: Failed");
    }
}

private boolean isListUploaded = false, isItemUploaded = false, isStoreUploaded = false, uploadingDone = false;


private class ListUpload extends Thread{

    @Override
    public void run() {
        isListUploaded = true;
        Log.i(TAG, "ListUpload Thread started");
        if(!uploadingDone)
            uploadingDone();
    }

}

private class ItemUpload extends Thread{

    @Override
    public void run() {
        Log.i(TAG, "ItemUpload Thread started");
        isItemUploaded = true;
        if(!uploadingDone)
            uploadingDone();
    }
}

private class StoreUpload extends Thread{

    @Override
    public void run() {
        Log.i(TAG, "StoreUpload Thread started");
        isStoreUploaded = true;
        if(!uploadingDone)
            uploadingDone();
    }

}

private ListUpload listUpload;
private StoreUpload storeUpload;
private ItemUpload itemUpload;

public void startUpload(){

    listUpload = new ListUpload();
    listUpload.start();

    storeUpload = new StoreUpload();
    storeUpload.start();

    itemUpload = new ItemUpload();
    itemUpload.start();

}

Thank you.

Answer 1

Skip the flags and add

listUpload.join();
storeUpload.join();
itemUpload.join();
// <BLOCK1>

at the end of startUpload(). Each call to join() will cause the calling thread to block until the given thread finishes.

Answer 2

I modified my source as claesv mentioned. I m posting my resultant code to show how this Thread.join method simplified my task. Hope will help someone.

private void uploadingDone(){

if( isItemUploaded && isListUploaded && isStoreUploaded){
    uploadingDone = true;
     //<BLOCK1>
    //TODO move to next screen
}else{
    Log.i(TAG, "uploadingDone: Failed");
    showFailureAlert();
}
}

// These flags are used to VALIDADTION success of uploading process. No need if you no need validation to move screen.

private boolean isListUploaded = false, isItemUploaded = false, isStoreUploaded =   false, uploadingDone = false;


private class ListUpload extends Thread{

@Override
public void run() {
    isListUploaded = true;
    Log.i(TAG, "ListUpload Thread started");
}

}

private class ItemUpload extends Thread{

@Override
public void run() {
    Log.i(TAG, "ItemUpload Thread started");
    isItemUploaded = true;
}
}

 private class StoreUpload extends Thread{

@Override
public void run() {
    Log.i(TAG, "StoreUpload Thread started");
    isStoreUploaded = true;
}

}

private ListUpload listUpload;
private StoreUpload storeUpload;
private ItemUpload itemUpload;

public void startUpload(){

listUpload = new ListUpload();
listUpload.start();

storeUpload = new StoreUpload();
storeUpload.start();

itemUpload = new ItemUpload();
itemUpload.start();

listUpload.join();
storeUpload.join();
itemUpload.join();

//Here comes the final block to execute after all threads finished
uploadingDone();

}

NOTE: Don't put thread.join() after immediate thread.start() consider this:

t1.start();
t2.start();
t3.start();
t4.start();

t1.join();
t2.join();
t3.join();
t4.join();